The invention relates generally to the field of techniques for manufacturing porous silicon. More particularly, the invention relates to the manufacture of photoluminescing porous silicon using spark erosion.
Silicon is widely used in the manufacture of microelectronic devices, but conventionally manufactured silicon is not suitable for light emitting diodes or lasers since it does not photoluminesce. It has recently been discovered that essentially porous silicon is photoluminescing and can therefore be used for light emitting devices . Porous silicon is generally characterized as an array of free-standing, crystalline silicon columns ranging from 2 to 100 nanometers in diameter with a large surface to volume ratio. Pore size and pore density varies.
It is known to create porous silicon by anodic etching of a silicon wafer in aqueous acid solutions, such as a solution containing hydrofluoric acid. Thin layers of porous silicon 3 to 7 microns in depth are produced this way near the surface of the silicon wafer. Examples of such techniques are given in Kinney et al. U.S. Pat. No. 4,532,700, and Katoh et al. U.S. Pat. No. 5,156,896.
Manufacture of porous silicon using anodic etching in hydrofluoric acid-containing aqueous solutions creates problems for research and for large scale manufacture in that the process introduces various contaminants into the silicon, as well as creating an environmental problem since the aqueous solutions used for this purpose are hazardous materials to work with and to dispose of.
It is known to use spark erosion in kerosene to shape or cut delicate materials. A high voltage spark generator creates in this case a large number of sparks which are directed over a particular area of the material. The sparks completely remove some material to create macro-scale holes, grooves, etc.
It is an object of this invention to provide a method for the manufacture of porous silicon layers on silicon wafers using a dry technique which does not involve either anodic etching or the use of acidic aqueous solutions.
It is a further object to provide such a method whereby the porous silicon layer is created by the technique of spark erosion.
It is a further object to provide a photoluminescing porous silicon layer on a silicon wafer by the method of spark erosion.